Electrical spark perforator for moving web



Jan.2s,1969 Komm l 3,424,895

ELECTRICAL SPARK PERFORATOR FOR MOVING WEB Jan. 28, 1969 A. K. OLSON3,424,895

ELECTRICAL SPARKPERFORATOR FOR MOVING WEB Filed Dec. 2, 1966 sheet 3 of;76. 624 F/G. 65

I F/c7165 l H6714 F/G 7.5

United States Patent O 1S Claims ABSTRACT OF THE DISCLOSURE An apparatusand method for electrically perforating a moving web are disclosedwherein the web is guided between a first electrode which continuallyslideably engages the web and a second electrode, the web beingsupported a predetermined distance from the second electrode by apressurized moving fluid film; and the discharge of the electrodes beingsynchronized with the rate of web advance. i

This invention relates to apparatus and method for perforating a movinglength of strip material and in one aspect to apparatus and method forelectrically perforating a rapidly moving web supported by a fluid filmbetween a pair of electrodes.

Perforation of a rapidly moving web by means of an electrical dischargeacross a pair of electrodes adjacent a moving web is known.

In one known spark recording system a web moving at a uniform rate isperforated as a means of recording information. The web is moved withina spark gap formed between a pointed electrode, which is positionednormal to and adjacent one surface of the moving web, and a rotatingelectrode, which physically contacts the moving web and is in spacedalignment With the pointed electrode. When a spark is produced acrossthe electrodes, the moving web is perforated in the vicinity of thepointed electrode at the instant the spark is produced. The web isadvanced at a uniform rate and the spark is produced at intervalsindependent of the rate of advance of the web.

Other known devices feed the moving web between an anvil and a diewherein the anvil supports a pair of electrodes adjacent the websurface. A high-voltage highcurrent electrical spark having a durationin the order of microseconds is discharged across the electrodes. Thegases produced by the spark are confined between the anvil and die. Theforce produced by the rapid expansion of the gas due to the electricaldischarge causes the moving web to be embossed or perforated in adesired manner. Improved spark discharge control means have beendeveloped to control more than one pair of electrodes thereby permittingseveral web perforations to be accomplished simultaneously.

Spark perforation of microscopic holes in stationary dielectricmaterials is known. The spark perforation is accomplished by a pair ofpointed electrodes placed in pressure contact, one on each side of thedielectric material to be pierced. Additionally, one of the pointedelectrodes is immersed in a dielectric fluid such that when anelectrical discharge is produced, the discharge travels .directlythrough the material being pierced thereby permitting holes to be placedin close proximity to each other. The fluid is utilized to prevent thespark discharge from occurring at any other location other than at thetip of the pointed electrode.

The known prior art apparatus and methods have certain disadvantages. Adisadvantage of the spark recording system is that the rotatingelectrode contacting the surface of the moving web has a large mass anda high 3,424,895 Patented Jan. 28, 1969 heat transfer coefficient. Whenan electrical discharge occurs between the electrodes, one of which isthe large rotating electrode, the resulting perforations have anonuniform axial diameter. This occurs because the rotating electrode,contacting the web surface, absorbs a substantial portion of the thermalenergy produced by the electrical discharge, which thermal energy wouldotherwise produce a perforation of uniform diameter.

The apparatus employing a die and an anvil has a disadvantage in thatseparate machined components are required to vary the diameter of theperforations. Further, the high voltage pulses require high currents inthe order of hundreds of amps. Because of the large current magnitudesand short burning times associated with such discharges, the resultingperforations have ragged edges and burrs.

The apparatus for electrically piercing microscopic holes in dielectricmaterials has the disadvantage that the electrodes must be brought intopressure engagement with the surface of the material to be pierced andone of the electrodes must be immersed in a dielectric fluid to preventflashover. Thus, the apparatus must include means for fixing theelectrode and workpiece together to prevent movement therebetween at thetime of the electrical discharge. A further disadvantage of thisapparatus is that the perforations cannot be continuously made on amoving dielectric material.

Other problems of the prior art devices are that certain of sparkperforators are energized by direct current voltage or by a fixedalternating current voltage such that a variance in the speed of themoving web results in a nonuniform density of holes per unit area as afunction of web speed. Further, a pointed electrode, when placed normalto and in continual contact with the material to be perforated, wearsand 'becomes rounded. As the electrode becomes rounded, hole placementin the dielectric material becomes uncontrollable. Thus, it is necessarythat fboth electrodes be sharply pointed and disposed opposite eachother. If point electrodes are utilized to contact a rapidly moving web,the pointed electrodes must be continually replaced or sharpened toinsure controllable perforations in the moving web.

This invention overcomes the disadvantages of the prior art by providinga sprak perforator utilizing a fluid film. The fiuid film supports arapidly moving web in a spark gap between two electrodes and provides athermal barrier for the discharge. One electrode is positioned at anangle to slideably contact one surface of the moving web. The otherelectrode, which is disposed in spaced v alignment from the oneelectrode to form the spark gap therebetween, has the moving web spacedtherefrom by means of the fluid film. The fiuid film serves a dualfunction as an air bearing and as a thermal barrier. The thermal barrierfunction of the uid film insures perforations of uniform axial diameterthroughout the entire web thickness.

Another advantage of this invention is that the frequency of theelectrical discharges between the electrodes can, as desired, besynchronized with the rate of advance of the moving web such thatperforations of a uniform density are produced in the longitudinaldirection of web movement at any web speed.

A further advantage of the present invention is that one of theelectrodes is preferably a pointed or needle electrode which isself-sharpening and need not be replaced even though the tip thereof isworn by the abrasive effect between the electrode and rapidly movingweb.

Another advantage of this invention is that the diameter of theperforations may be precisely controlled by varying the duration, thevoltage and current of the electrical discharge. By utilizing theteachings of this invention, perforations having a wide range ofdiameters can be made in a web wherein the web can be either stationaryor moving over a wide range of speeds from substantially zero feet perminute up to and in excess of 800 feet (244 meters) per minute.

Yet another advantage of the present invention is that a method ofperforating a moving web is provided wherein the perforations may be ofuniform axial diameter and without ragged edges and burrs.

Briefly, the apparatus for perforating a rapidly moving web includes afirst and a second electrode. The first electrode is positioned at anangle to the longitudinal direction of web movement and continuallyslideably contacts one surface of the web. The second electrode isspaced from the first electrode. The second electrode, or an auxiliarysource, comprises means for forming a fluid film in the spark gap whichsupports the web a predetermined distance from the second electrode. Apower means is connected between the first and the second electrodes andproduces an electrical discharge lacross the spark gap which perforatesthe web. The apparatus further includes means which are connected to thepower means for synchronizing the electrical discharge with the rate ofadvance of the web.

The above and further advantages of the present invention will becomefully apparent when considered in light of the following detaileddescription and drawing.

FIGURE 1 is a diagrammatic illustration partially in block form showingone embodiment of a spark perforator utilizing the teachings of thisinvention;

FIGURE 2 is 'a graph illustrating a waveform of the current as afunction of time of the electrical discharges of the spark perforator;

FIGURE 3 is a side view of a needle electrode used in one embodiment ofthe spark perforator;

FIGURE 4 is a diagrammatic illustration showing the relationship betweenthe moving web and electrodes across which an electrical discharge isproduced;

FIGURE 5 is a side view of a needle electrode support assembly;

FIGURES 6A, 6B and 6C are diagrammatic illustrations of the electricaldischarge between a needle electrode and a plenum at various stagesduring web perforation;

FIGURES 7A and 7B are diagrammatic illustrations of the wearing of aneedle electrode which slideably engages a rapidly moving web; and

FIGURE 8 is a schematic diagram partially in diagrammatic illustrationshowing a high voltage supply and a triode vacuum tube for synchronizingthe electrical discharge with the rate of advance of the web.

In the diagrammatic illustration of the spark perforator of FIGURE 1, arapidly moving web 12 is guided along a predetermined path around ajournalled roller 14. The moving web 12 is driven around the roller 14by means of a web drive 16 operatively coupled to a first set of rollersincludingl a driving roller 18 'and an idling roller 20. The roller 20forms a nip with driving roller 18 such that counterclockwise rotationof roller 18 advances the web across the surface of roller 14. A secondset of guide rollers 22 and 24 direct the moving web such that itfollows the arcuate surface of roller 14.

The roller 14, in one preferred embodiment, is secured in apredetermined position and the moving web 12 slideably advances acrossthe surface thereof. However, the roller 14 is constructed such thatwhen it is unclamped it is permitted to freely rotate as the web 12advances thereacross.

The roller 14 has a thin cylindrical outer wall 26 enclosed by endmembers 28, only one being shown due to cross sectioning of the roller14. The outer wall 26 and the end members 28 form a fluid chamber 30within the interior of roller 14. Each of the end members are journalledat support members 32 to permit either clamping or rotation of roller14. Further, the roller 14 is constructed such that about one-half ofthe outer wall 26, or about a 180 sector, has a plurality of apertures34 extending therethrough between the external periphery of outer wall26 and chamber 30. This 180 sector forms a plenum 36. It is anticipatedthat more or less than a sector may contain the apertures 34. Forexample, some applications may require that the plurality of apertures34 be provided about the entire periphery of the roller 14. In thisapplication, the apertures would be aligned relative to the electrodessuch that a portion of the roller surface is always positioned in spacedalignment with the electrodes, to be described hereinafter, to insureperforation of the web.

When the roller 14 is clamped or secured from rotation, the plenum 36 ispositioned adjacent the moving web 12. A source of positive fluidpressure 38 is operatively connected via a line 40 to the support member32 such that a positive pressure is introduced into the chamber 30. Thepositive pressure in chamber 30 forces fluid through apertures 34against the undersurface of the web 12. Hereinafter, the side of themoving web 12 near the outer wall 26 shall be referred to as theundersurface while the opposite side thereof shall be referred to as theouter surface. The fluid directing through apertures 34 of plenum 36 isconfined between the undersurface of the moving web 12 and the outerwall 26 and forms a fluid film 42.

As mentioned hereinbefore, the roller 14 can be unsecured such that theroller freely rotates as the web 12 advances across the surface thereof.

When the roller 14 is permitted to freely rotate together with therapidly moving web 12, the rapidly moving web 12 generates a laminarflow of fluid due to the frictional interaction between the moving weband the surrounding fluid. 'Ihe rapidly moving web 12 causes the laminarflow of fluid to be directed between the outer wall 26 of roller 14 andthe moving web 12. The laminar flow of fluid creates a hydrodynamicforce which resiliently supports the web 12 a predetermined distancefrom the periphery of outer wall 26 forming the fl-uid film 42.Concurrently, the roller 14 is rotated by the force of the moving fluid.rIlhe peripheral velocity of the outer wall 26 is substantially the sameas the linear velocity of the advancing web 12. Further, in someapplications it may be desirable to permit the roller 14 to freelyrotate while the source of positive pressure is utilized to aid informing the fluid film 42. In this instance, the roller 14 would have aplurality of apertures 34 about its entire periphery.

In any application, i.e. when the roller 14 is secured in apredetermined position with plenum 36 adjacent the web 12 and a positivesource of fluid pressure is utilized, or when roller 14 is permitted tofreely rotate, or when the roller 14 is permitted to freely rotate and apositive source of fluid pressure is utilized, the confined fluid formsthe fluid bearing or fluid film 42 between the outer wall 26 or roller14 and the undersurface of moving web 12. 'I'he fluid filmI 42 spacesthe moving web 12 a predetermined distance from. the roller 14. Thespaced distance of web 12 from roller 14 is a function of tensionproduced by the web drive 16 in cooperation with driving roller 18 andidling roller 20.

It is anticipated that equivalent apparatus could be used in performingthe function of the roller in various modes of operation. The use of aroller member in cooperation with a posit-ive pressure source isintended to be only an illustrative embodiment of one mode of thisinvention.

A needle electrode 44 having a conical tip member 46 and a conductiveresilient support means 48 is positioned to slideably engage the movingweb 12, said needle electrode being positioned at yan angle 9 to thelongitudinal direction of web movement. In this embodiment, the needleelectrode 44 forms a first electrode and the roller 14 forms a sec-ondelectrode. It is anticipated that the second electrode could be pointedwith the tip thereof positioned frotm the surface of roller 14 and intothe fluid film 42. Such an arrangement would increase the voltagegradients between the electrodes for perforation of materials havinghighkilovolt dielectric strength. The needle electrode 44 and the roller14 are spaced to form a spark gap therebetween through which the webadvances. The conductive resilient support means 48 permits the needleelectrode tip 46 to yieldably slideably engage the outer surface of theweb 12. The needle electrode 44 is electrically connected in seriescircuit to a resistor 50 having a high ohmic value.

Hereinafter, the remainder of the discussion will be directed to theoperation of the spark perforator wherein the roller is seoured orclamped such that the plenum 36 of outer wall 26 is adjacent the movingweb 12. Thus, the flulid llrn 42 is formed by the liuid directed throughaperture 34 and between the under side of web 12 and wall 26. Theprinciples of operation described in connection with this condition areequally applicable when the roller 14 is permitted to freely rotateeither with or without the source of positive pressure 38 aiding in theformation of the fluid iilm 42.

The source of positive lluid pressure 38 is selected to be of suicientpressure to form the fluid nlm 42 in the spark gap beween the needleelectrode 44 and the roller 14 to space the web a predetermined distancefrom the wall 26. p

An electrical discharge is produced across the tip 46 of needleelectrode 44 to plenum 36 by applying a high voltage pulse across theresistor 50. The electrical discharge or spark burns a hole through theweb 12 beginning at a point at the end of the electrode tip 46. As theweb advances, the electrical discharge burns a perforation, having apreselected uniform axial diameter, through the thickness of the web 12.

The electrical energy for producing the high voltage pulse is obtainedfrom power means 52 which may be a high voltage power supply. The powermeans 52 is connected via line 54 to the roller 14 establishing a commonreference potential therebetween. A switching means 56 is electricallyconnected between the power means 52 via a conductor 58 and the resistor50 by means of a conductor 60. When the switching means 56 is actuated,an electrical cirouit is completed between power means 52, conductor 58,switching means 56, conductor 60, resistor 50, resilient means 48, tip|46, and across the spark gap to the roller 14, conductor S4 back to thepower.

means 52. The resulting electrical discharge in the spark gap betweenneedle electrode 44 and roller 14 perforates the moving web 12.

Switching means 56 is controlled in synchronism with the Vrate ofadvancement of the web 12. Thus, the spark perforator is capable ofperforating the moving web 12 at a unifonm density regardless of webspeed. This synchronization is accomplished, in this embodiment, byconnecting a pulse generator 62 to guide roller 24. The pulse generator62 produces a series of output pulses as a function of the rate ofadvance of the web, which is determined by t'he rotations per minute ofthe guide roller 24. The output pulses produced by the pulse generator62 are `applied to a counter 64. Counter 64 produces a control pulseafter receiving a predetermined number of output pulses from the pulsegenerator 62. The counter 64 applies the control pulses to a controlmeans 66. The control means 66 conditions switching means 56 with aswitching pulse in response to each control pulse. The switching means56, when triggered by switching pulse, connects the power means 52 tothe resistor 50. By synchronizing the electrical discharge acrosselectrode 44 and roller 14 with the rate of advance of the web, thedensity of perforations per unit area on the web will be uniformregardless of the rate of advance of the web.

The electrical discharge produced by switching means 56 in synchronismWith the advancing web is determined 'by the control means 66. Animportant feature of the spark perforator is that the resultingelectrical discharge produced by switching means 56, in response to aswitching pulse from the control means 66, is of a relatively low powerlevel. This feature is important since the prior art devices requiredpulses having current magnitudes in the order of hundreds of amps andextremely short time durations in the order of microseconds.

In the present invention, the pulses have current magnitudes in theorder of milliamps and pulse durations in the order of milliseconds. Atypical waveform of the spark perforator discharge current as a functionof time is illustrated in the graph of FIGURE 2. The graph of FIGURE 2comprises two electrical discharge waveforms 68 and 70 wherein the timeinterval therebetween is a function of web speed. If the web isadvancing at a high rate, the duration between pulses is extremelyshort. Inversely, if the web is advancing at a slow rate, the timeinterval between the pulses is greater thereby maintaining uniformperforation density regardless of web speed.

Referring now, for example, to waveform 68 illustrated in the graph ofFIGURE 2, at the beginning of the electrical discharge, particularlywith the leading edge thereof occurring at time T1, the dischargecurrent may be in the order of about six milliamps. The eract currentmagnitude is a function of discharge voltage, the material to beperforated and the thickness of the fluid film. The pulse duration maybe about two and one-half milliseconds and the trailing edge of thedischarge is illustrated at time T2. At time T2 the current may decreaseto a magnitude less than the original starting current. The diameter ofthe resulting perforation can be made larger by increasing the pulseduration. When the pulse duration is increased, the difference betweenthe beginning discharge current magnitude and the dischar-ge currentmagnitude at the end thereof increases. Thus, the maximum pulse durationwould be dependent upon the minimum current required to burn the movingweb 12 after the initial perforation is accomplished by the leading edgeof the discharge pulse at time T1.

The power consumption required for perforating each hole in the movingweb is substantially decreased due to the uid film 42 which functions asa thermal barrier between the web 12 and the roller 14. The fluid film42 prevents the roller 14 from absorbing thermal energy from theelectrical discharge thereby permitting substantially all of the thermalenergy of the portion of the arc passing through the web to be utilizedin perforating the web 12.

In one embodiment, the web drive 16 provides a tension in the range of`about two pounds per inch (about .36 kilograms per centimeter) of webwidth while moving the web at speeds up to about 800 `feet (about 244meters) per minute. The clamped roller 16 had a diameter of about veinches (about 12.7 centimeters). The web was a .00125 inch (32 micron)thick paper. The iluid lilm 42 may be, for example, an air bearing, aninert gas bearing or the like of up to about .030 inch (about .75millimeter) thickness but may be normally in the range of about .001 to.005 inch (about .O3 to .13 millimeter). An air pressure of about two tofive pounds per square inch (about to 350 grams per square centimeter)was used to space the pap-er from the roller 14, which roller was madefrom one-eighth inch (3.2 millimeter) metal. The needle electrodes `wereconstructed of stainless steel. A spark perforator having the abovetypical characteristics is capable of perforating holes which are lessthan one micron in diameter at a density of about 64 holes per squareinch (about 10 holes per square centimeter). In one operation,perforations of about .0016 inch (about 40 microns) were made in themoving web 12. The power means 52 was about 6,000 volts and the pulseduration would vary from about 1.3 to 4.5 milliseconds. The angle 9 mayvary from normal to the outer surface of the web 12 down to about lessthan ten degrees with an angle of 45 degrees being preferred.

FIGURE 3 is a front view of the needle electrode 44 illustrating thatthe conductive resilient support means 48 may be a stainless steelcoiled spring soldered to a stainless steel tip46. The soldering wasaccomplished by using a solder comprising 60 percent tin and 40 percentlead and a soldering flux for stainless steel. v.

Referring now to FIGURE 4, the operation of the spark perforator isillustrated vwith the electrical discharge 74 at an intermediate pointwhen the electrical discharge is perforating-the web 12. The needleelectrode 44 is supported in aneedle electrode support 76 which iscircular in cross-section. The support 76 has an elongated opening 78extending therethrough into ,which the needle electrode 44 is inserted.The support 76 has a tapped opening 80 which is normal to opening 78.Thetapped opening 80 receives a set screw 82 which is advanced intocontact with spring 4 8 to removably support the needle electrode 44 inopening 78. The spring 48 permits the tip 46 of needle electrode 44 toyieldably engage the outer surface of web 12.'

The fluid film 42 is an important part of this invention in that itfunctions as a thermal barrier between the web 12 and the roller 14. Thefluid film 42 provides a reduced coefficient of sliding .frictionbetween-the web 12 and roller 14 such that the web can be driven in alongitudinal direction at speeds in excess of 800 feet I(244 meters) perminute. In the absence of the uid film 42, the moving web 12 would beurged into slideable engagement with the roller 14 with the tip 46 oftheneedle electrode 44 slideably engaging the outer surface of web 12. Ifan electrical discharge occurs between electrode tip 46 and roller 14undersuch conditions, a perforation would be made in the web 12.However, the axial diameter of the perforation of the undersurface ofweb 12 contacting roller 14 would be substantially less than the axialdiameter of the perforation onthe outer surface of the web 12 adjacentthe ti-p 46 ofthe needle electrode 44.

By placing the lluid lm 42 between themoving web 12 and roller 14,perforations of uniform axial diameter without burrs and ragged edgesare formed. The iiuid film V42 acts as a thermal barrier and the heatgenerated by an electrical discharge 74 occurring between the tip 46 ofelectrode 44 .and roller 14 is retained within the localized larea ofthe web being perforated. In the absence of the fluid film 42, theroller 14 absorbs thermal energy from the electrical discharge 74 such`that only a part of the thermal energy can be used for perforating theweb 12 thereby resulting rin the taperedhole.I Thus, introduction of aliuid lilm 42.between the rapidly moving ,web 12;,and the secondelectrode or roller 14 not onlyreduces the coeicient of sliding frictiontherebetween but. also provides a thermal barrier such that a rapidlymoving `web, 12 can be perforated at a uniform density with perforationsof uniform axial diameter throughout the entire thickness of the web 12.

The sizeof the perforation in the moving web can be controlled byvarying both the magnitude of current flowing between needle electrode44 and roller 14 and the duration of the pulse. The maximum high voltagepulse duration is limited by the length to which the electricaldischarge 74'can be extended as the web 12 advances before the dischargeis extinguished. The length of the electrical discharge 74 is determinedby the maximum ionized path which can be sustained by the source ofpotential through a perforation which is continually moving` away fromthe electrode tip 46. If the high voltage pulse duration exceeds thislimitation, the electrical discharge 74 could possibly restrike andperforate the web 12 in an undesired location.l

`FIGURE isl a side viewtof a needle electrode assembly ,84 having ahousing l86 which encloses the needle electrode support 7 6. Theneedleelectrode support 76 is an insulating elongatedmember having acircular cross-section as described in FIGURES and includes a pluralityof spaced elongated openings 78 therethrough such that a plurality ofneedle electrodes can be disposed along the width of the moving web 12.

A longitudinally extending member 88 having an 8 g elongated openingthereinwith arcuate edges is fastened to the housing 86 by means offasteners such asscrews 90. The member 88 receives thesupport 76 thereinsuch that the electrode tip 46 extends through its opening. When thescrews 90 are advanced into the housing 86, the member 88 secures thesupport A76 in the desired position such that electrode tip 46 yieldablyslideably engages the outer surface of web 12. An arcuate-shaped member92 isvtixedly connected to the housing 86 by means of ,screws 94, one ofwhich terminates in an electrode terminal 96. Further, thearcuate-shaped member 92 is positioned around the periphery of support76 to slideably contact and complete an electrical.circuitbetween theportion of spring 48 ex-` tending from opening 78 opposite the tip 46and resisto 50.

The entire needle electrode assembly. 84 iswrigidly supported by meansof housing support member 98 which member is fastened by a fastener 100`against la channel member 102. The channelmember 102 is ,constructed tohave a plurality of individual wiringV terminals 104 which wiringterminalsare subsequently connected to the resistor 50. Separate highvoltage conductors 106 elec. trically connect each wiring terminal 104to electrode terminal 96.l .v As indicated hereinbefore, electrode tip46 slideably engages the outer surface of the moving web 12 at an angle9 to the longitudinal direction of movementof the web. The angle 9 canbe adjusted by withdrawing screws 90 froml the housing 86 such that themember 88 is loosened to allow the needle electrode support 76 to berotated therein. As the support 76 is rotated to position theelectrodetip 46 at any desired angle and the screws 90 retightened, the spring 48slideably contacts the arcuate-shaped member 92 thereby insuring acomplete electrical connection between the needle electrode 44 and theremainder of the high voltage circuit. FIGURES 6A, 6B and 6C arediagrammatic representations Of the electrical discharge V74. Theelectrical discharge isv shown in FIGURE 6A as it commences, `in FIGURE6B at approximately Athe mid-point of the e1ectrical discharge and inFIGURE 6 C just' prior to termination ofthe electrical discharge. InFIGURE 6A, when the electrical discharge is produced,ia perforation 108having an initially small diameter is produced in the web 12 located atthe electrode tip `46 of electrode 44. When the electrical discharge 74occurs, the dielectric strength of the moving web 12 and the portion ofthe iiuid film 42,between the web 12 and outer wall 26 ofv roller 14isexceeded forming an ionized conductive path for the discharge 74fromelectrode tip 46 to outer wall 26. As the electrical discharge v74continues, the diameter of the perforation 108 increases as the webmoves relative to the outer wall 26.

This can be seen by referring to FIGURE 6B wherein the perforation 108is disposed lfrom the electrode tip 46of needle electrode 44 and thelength of the electrical discharge 74 is increased. As the length of theelectrical discharge 74 increases, the discharge 74 continually ionizesthe localized portions of the liud film 42 between web 12 and outer wall26. The diameter of perforation 108 of FIGURE 6B is increased comparedto that of FIGURE 6A. FIGURE 6C illustrates the final position of theperforation 108 just prior to extinction of the discharge 74. The lengthof the discharge 74 is substantially longer thanY that of FIGURE 6B, andwhen terminated the perforation 108 will be spaced from the electrodetip 46 of electrode 44. When a subsequent high voltage pulse is appliedto electrode 44, perforation 108 will be spaced sufficiently fromelectrode tip 46 of electrode 44 such that a subsequent perforation ismade in web 12 by a subsequent discharge 74. If perforation 108 is notspaced sufficiently from electrode tip 46 of electrode 44 at the time ofa subsequent electrical discharge, the discharge would ionize a path toouter wall 26 through the same perforation 108 whereupon web 12 wouldnot be perforated.

Since the electrode tip 46 continually slideably engages the rapidlymoving web 12, the sharp point of the tip 46 illust-rated in FIGURE 7Awill subsequently be Worn to a tapered point illustrated in FIGURE 7B.However, the electrode 44 is disposed at an angle G relative to thelongitudinal direction of movement of the web 12 and as electrode tip 46is Worn, the tip 46 forms a sharp trailing edge 110 which eng-ages theouter surface of web 12. When the discharge 74 is produced, it ernanatesfrom trailing edge 110 which functions as a pointed electrode. This isan important feature of this invention in that as the needle electrodewears, the resulting tapered point will still operate properly and theelectrode need not be replaced.

Referring now to the schematic diagram of FIGURE 8, each needleelectrode 44 is connected through a resistor 50 having a high ohmicvalue of about one megohm. A second resistor 112 having a substantiallylower ohmic value, in the range of about 27,000 ohms, is connected inseries circuit with resistor 50. Connected in parallel to the secondresistor 112 is a neon lamp 114, -which lamp is connected in seriescircuit with a current limiting resistor 116. Resistor 112, resistor 50,needle electrode 44 and neon lamp 114 are energized by a conductor 118,which conductor is electrically connected to a switching means,particularly a high voltage triode vacuum tube 120. The resistor 116 isinserted in series circuit with the resistor 50 to provide a smallvoltage drop of sufficient magnitude to ignite neon lamp 114. Each neonlamp 114 is ignited providing a visual indication that a spark is beingproduced each time an electrical discharge occurs between each needleelectrode 44 and the second electrode or outer wall 26. In the eventthat one of the needle electrodes fails to produce an electricaldischarge when energized, neon lamp 114 will not be ignited therebyproviding a visual indication of the malfunction.

Tube 120 is connected to a high voltage power supply 124. When tube 120is rendered conductive, the tube 120 electrically connects the highvoltage power supply 124 to conductor 118. Conductor 118 applies thehigh voltage across the parallelly connected needle electrodes 44causing the electrical discharge between each needle electrodev 44 andouter wall 26 of roller 14. Outer wall 26 is electrically connected tothe high voltage power supply 124 by means of conductor 126 therebycompleting the high voltage circuit.

The conduction of the 120 may be controlled by a oneshot rnonostablemultivibrator 128 in response to a control pulse applied thereto via aninput 130. The high voltage pulse duration is determined by the resettime of multivibrator 128.

When the high voltage `pulse is applied via resistors 112 and 50 to theneedle electrodes 44, the capacitance between each high voltage lead andground stores a charge. This charge is removed by means of a bleederresistor 132, which resistor is electrically connected between conductor118 and the high voltage power supply 124.

The high voltage -pulse duration is controlled by varying the on time ofthe multivibrator 128. The interval between pulses is determined by thefrequency of control pulses applied to input 130 from a pulse generatingand counting circuit such as that of FIGURE l. The resistors 50 arenecessary in this spark perforator so that each of the needle electrodeswill generate an electrical discharge regardless of whether or not theother electrodes are discharged. After an electrode has producer adischarge, its resistor 50 develops a voltage drop thereacross ofsufiicient magnitude to keep the voltage on conductor 118 at a highvoltage level such that the other electrodes can produce a discharge. Inthe absence of resistors 50, if one of the electrodes discharged priorto the other electrodes, the voltage on conductor 118 would be reducedsubstantially to ground potential such that the other electrodes couldnot produce an electrical discharge.

Having thus described the inventive spark perforator, it is to beunderstood that various modifications will be apparent to one havingordinary skill in the art and all such modifications are contemplated aswithin the scope of the appended claims.

What is claimed is:

1. Apparatus for electrically perforating a moving web comprising afirst electrode positioned at an angle to the longitudinal direction ofweb movement for continually slideably engaging one surface of said web;

a second electrode spaced from said first electrode for forming a sparkgap therebetween through which said web advances;

means for supporting said web on a moving fluid film having sufiicientpressure to space said web a predetermined distance from said secondelectrode;

power means connected between said first and second electrodes forproducing an electrical discharge thereacross having a potentialsufficient to at least perforate said web; and

means connected to said power means for synchronizing said electricaldischarge with the rate of advance 0f said web.

2. The apparatus as set forth in claim 1 wherein said first electrodeincludes a conical tip member which slideably engages said one surfaceof the web such that as said tip becomes worn the trailing edge thereofremains pointed independent of electrode wear, and wherein said secondelectrode is a continuous surface.

3. The apparatus of claim 1 wherein said iirst electrode is a stainlesssteel needle electrode supported by a conductive resilient means whichyieldably urges the tip of said needle electrode into continualslideable engagement with said one surface of the web, and wherein saidsecond electrode is a metal plenum having an outer surface formed with aplurality of apertures therethrough, said apparatus further including asource of positive iiuid pressure communicating with said web supportingmeans to direct fiuid under pressure through said apertures forproducing a iiuid film which supports said web a predetermined distancefrom said plenum outer surface.

4. The apparatus of claim 1 wherein said first electrode is a stainlesssteel needle electrode supported by a conductive resilient means whichyieldably urges the tip of said needle electrode into continualslideable engagement with said one surface of the web, and wherein saidsecond electrode is a metal roller having a metal outer Wall and adaptedto freely rotate as said web is advanced thereacross whereupon saidadvancing web in cooperation with said roller causes a laminar fiow offiuid to be confined therebetween which supports said web apredetermined distance from said roller outer wall.

5. The apparatus of claim 4 wherein said metal roller outer wallincludes a plurality of apertures extending therethrough and whereinsaid metal roller outer wall encloses a hollowed-out area therein forforming a fluid chamber, said apparatus further including a source ofpositive fluid pressure communicating with said fluid chamber to directfluid under pressure through said apertures for producing a fluid filmwhich supports said web a predetermined distance from metal roller outerwall.

6. The apparatus of claim 5 wherein said metal roller incudes means forclam-ping said roller in a predetermined position whereby the advancingweb slideably advances thereacross.

7. The apparatus of claim 1 wherein said synchronizing means includespulse generating means responsive to said moving web for producingoutput pulses which are a function of the rate of advance of said web;

counting means operatively connected to receive said output pulses fromsaid pulse generating means for producing a control pulse upon receivinga predetermined number of output pulses;

control means operatively connected to said counting means for producinga switching pulse in response to said control pulse, said switchingpulse having a duration which determines the high voltage electricaldischarge duration which occurs between said electrodes; and

switching means connected between said power means and said iirstelectrode which is responsive to said control means for connecting saidpower means to said rst electrode in response to and for the duration ofsaid switching pulse.

8. Apparatus for perforating a rapidly moving web comprising a pluralityof aligned spaced needle electrodes positioned at an angle to thelongitudinal direction of web movement for continually slideablyengaging one surface of said moving web;

a continuous surface second electrode having a plurality of aperturestherethrough, said second electrode being spaced from said plurality ofneedle electrodes for forming a plurality of spark gaps between each ofsaid needle electrodes and said second electrode and for directing saidweb along a predetermined path through said spark gaps; K

means including a source of fluid under a positive pressure operativelyconnected to said second electrode and communicating with said aperturesfor forming a fluid lm which supports said moving web a predetermineddistance from said second electrode;

means including a high voltage power supply yconnected between each ofsaid needle electrodes and said second electrode for simultaneouslyproducing a high voltage electrical discharge across said spark gaps ofa sufficient potential to perforate said web; and

means connected to said power supply means for synchronizing saidplurality of electrical discharges With the rate of advance of said web.

9. The apparatus of claim 8 wherein said plurality of needle electrodesare supported in an electrode assembly support member by means ofconductive. resilient means which yieldably urge the tips of theelectrodes into continual slideable engagement with said one surface ofthe web.

10. The apparatus of claim 8 further including web driving means foradvancing the web in a longitudinal direction of movement between saidneedle electrodes and said second electrode, said web driving meansbeing capable of selectively driving said web from a slow speed to arapid speed.

11. The apparatus of claim 8 wherein said synchronizing means includespulse generating means responsive to said moving web for producingoutput pulses which are a function of the rate of advance at which saidweb driving means advances said web;

counting means operatively connected to receive said output pulses fromsaid pulse generating means for producing a control pulse upon receivinga predetermining number of out-put pulses from said pulse generatingmeans; control means operatively connected to said counting means forproducing a switching pulse in response Y Y 12 l to said control pulse,said switching pulse having a duration which determines the electricaldischarge duration which occurs between ,each of said needle electrodesand said second electrode; and switching means connected lbetween saidhigh voltage power supply andV each of ysaid needle electrodes which isresponsive to said control means for connecting said high voltage powersupply simultaneously to.ea ch of said needle electrodes in response t0and for the duration of said switching pulse. 12. The apparatus of claim8 further including a plurality of high ohmic value resistors one ofeach of which is electrically connected in series `circuit relationshipwith one of said needle electrodes. 13. The apparatus of claim 12further including a plurality of low ohmic value resistors one of eachof which is electrically connected in series circuit relationship witheach of said high ohmic value resistors and said needle electrodes; anda plurality of neon lamps one of each of which is electrically connectedin parallel circuit relationship witheach of said low ohmic Vvalueresistors, said low ohmic value resistors producing a voltage dropthereacross of suicient magnitude toenergize said neon lamps toprovide avisual indication when its associated needle electrode produces anelectrical discharge. 14. A method for perforating a moving webcomprising the steps of guiding `said web between a rst electrode, whichslideably engages one surface thereof, and a second electrode spacedfrom said `lirst electrode forming a spark gap therebetween; producinga, moving fluid lm between said web and said second electrode undersucient pressure for supporting said web a predetermined distance fromsaid second electrode;- generating a high voltage electrical dischargebetween said iirst and second'electrodes of a potentialsucient toatleast perforate said advancing web; and synchronizing the generatingof said high voltage elecktrical discharge with the rate of advance ofsaid web. 15. The method of claim 14 wherein said moving web is guidedbetween a plurality of ne'edle electrodes and a second electrode over alluid film which supports said web a predetermined distance from saidsecond electrode, and further comprising the step of t driving said webover said uid iilm between said needle electrodes and said secondelectrode over a range of web speeds.

References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, PrimaryExaminer. V. Y. MAYEWSKY, Assistant Examiner.

